Ultrasound assessment of diaphragmatic function in type 1 spinal muscular atrophy

Objective To investigate ultrasound features of diaphragm motion and function in type 1 spinal muscular atrophy (SMA‐1) patients. Design Prospective study. Patients The study cohort included SMA‐1 children younger than 18‐year‐old. Control subjects included type 2 and type 3 SMA and other neuromuscular disorders younger than 18‐year‐old. Methodology Diaphragm ultrasound evaluating diaphragmatic excursion, speed of diaphragmatic contraction, duration of the respiratory cycle, inspiratory/expiratory relationship, end‐inspiratory and ‐expiratory thickness, thickening fraction, and pattern of contractility. The interrater reliability for each variable was established by calculation of Cohen's k coefficient. Results Twenty‐three SMA‐1 patients and 12 controls were evaluated. Diaphragm ultrasound values were within normal ranges in all study cohort patients and no difference was found with controls. There was a gradient of diaphragm function with SMA 1.9 subgroup having the best and SMA 1.1 having the worst parameters, particularly in end‐inspiratory thickness and diaphragmatic excursion (P = .031 and P = .041, respectively). Seventy‐four percent of SMA‐1 patients had a dysmotility pattern of diaphragm contraction, mostly represented in SMA 1.9 subgroup (P = .001). This pattern was observed in 92.8% of children on noninvasive ventilation (NIV) for less than 16 hours/d of and in 20% patients with invasive ventilation or NIV for more than 16 hours/d (P = .027). The dysmotility pattern was never observed in the control group. The levels of interobserver agreement were high for “diaphragm irregularities,” “inspiratory/expiratory relationship,” and “diaphragm thickness,” and good for the other variables. Conclusions Ultrasound can be used to evaluate diaphragm function and contractility in SMA‐1 children, providing additional information to the clinical examination and functional respiratory tests, describing a characteristic contractility pattern in these patients. Longitudinal studies are needed to understand the impact of diaphragm dysmotility and other parameters on long‐term outcome in SMA‐1 patients.